The vascular system of the eye represents a compromise between the needs for efficient supply of nutrients to the intraocular tissues and the requirement of good optics. The solution is adequate in young and healthy individuals but involves great risks for local nutritive problems at higher age and in many diseases affecting the blood vessels. Glaucoma, maculopaties, diabetic retinopathy, and cataracts are a few examples. Inadequate nutrition of the retina, including the intraocular part of the optic nerve, of course may cause cell death. Factors contributing during the critical period when nutrition is inadequate are release of excitatory amino acids and/or influx of excess Ca ions into the cells, which may overstimulate the metabolism. There are reasons to suspect that damage may also be induced by flickering light due to overstimulation of cells. Restituted blood flow after a period with inadequate flow may also introduce a problem; reperfusion of partially ischemic parts of the retina may result in the formation of free radicals with profound effects on cell membranes and enzymes. The aim of our studies is to elucidate the relative roles of the choroidal and retinal blood vessels in supplying nutrients to the retina and to analyze also the requirements of the retina under different conditions. A modification of Sokoloff's deoxyglucose method is used to identify the conditions that seem to be metabolically stressful for the retina and the optic nerve head and to investigate if they involve an increased risk for the retina under conditions of reduced nutrient supply. High intraocular pressure is one of the factors that tend to damage the retina and optic nerve head. Pharmacological means to reduce the IOP are still inadequate in many cases of glaucoma, which motivates further studies on the control of aqueous humor formation and drainage. An isotope dilution method permitting simultaneous, bilateral, near- continuous determination of aqueous humor flow is used in these studies.